Metal additive manufacturing in a direct energy deposition (DED) method is a process of welding metal on an area to be machined by supplying a metal material such as metal powder or metal wire while locally melting the metal material by emitting a laser beam onto the metal material. Since this technique is characterized in high flexibility of shaping, which enables a shape that is difficult to produce by cutting methods to be easily formed.
In the metal additive manufacturing, a numerical control (NC) device that adjusts process parameters such as a laser output, a supply amount of metal powder or metal wire, and also the temperature of a molten pool is called a deposition condition control device. In addition, a pool of molten metal resulting from melting of a base material is called a molten pool. When metal additive manufacturing is performed by using a deposition condition control device, machining programs are typically created by a computer aided manufacturing (CAM). A machining program describes information on a machined shape, a laser output, and a supply amount of metal powder or metal wire. The deposition condition control device reads the machining program, and computes a movement path of a portion to be machined, which is part of the base material, to be irradiated with the laser beam. Furthermore, the deposition condition control device performs processes including acceleration/deceleration, and computes interpolation points, which are command points per unit time on the movement path. Respective drive shafts of the numerically-controlled machine tool are controlled with the computed interpolation point data, and the portion to be machined or the laser irradiation position is moved to a target position, so that the portion to be machined is irradiated with laser beam of the laser beam output value described in the machining program. The portion to be machined, which is part of the base material, is molten to form a molten pool, to which the metal powder or metal wire is supplied at a rate described in the machining program. After a lapse of certain time, the portion to be machined is resolidified with deposited metal, and additive manufacturing is thus carried out. In this process, for obtaining a target shape or a fine structure, the portion to be machined or the laser irradiation position needs to be moved to a target position, and process parameters such as the laser irradiation amount to the portion to be machined, the supply amount of metal powder or metal wire, and also the temperature of the molten pool need to be adjusted. In Patent Literature 1, for example, the laser output and the supply amount of metal powder or metal wire are thus adjusted in view of the temperature of the molten pool.